Jet propulsion of helicopters



Dec. 31, 1957 Y DOBLHOFF 2,818,223

JET PROPULSION OF HELICOPTERS Original Filed April 9, 1947 W 2Sheets-Sheet 1 Lb I INVENTOR ATTORNEYS Dec. 31, 1957 F, DOBLHO'FF2,818,223

JET PROPULSION 0F HELICOPTERS Original Filed April 9. 194'? 4 2 Sheets-Sheet 2 fW/ED/P/Cl/ L DOBLHa;

" ATTORNEYS I, N I

- I 3 INVENTOR United States Patent JET PROPULSION or HELICOPTERSFriedrich List Doblholf, Zell am See, Austria, assignor to The FaireyAviation Company Limited, Hayes, Middlesex, England Original applicationApril 9, 1947, Serial No. 740,366, now Patent No. 2,667,226, datedJanuary 26, 1954. Divided and this application January 27, 1953, SerialNo. 342,622

3 Claims. (Cl. 244-1719) 'This application is a division of myapplication Serial No. 740,366, filed April 9, 1947, for Jet Propulsionof Helicopters, now Patent No. 2,667,226.

This invention relates to improvements in, reaction propulsionparticularly adapted for use with helicopters, but also useful withordinary aircraft.

It is known that the use of reaction propulsion in helicopters permitsthe avoidance of the couple which occurs with the mechanical drive ofthe rotors, and the avoidance of the need for anti-couple devices suchas tail propellers and double rotors. Reaction propulsion also does awaywith the weight, the costs of construction, and the maintenance ofreciprocating motors, and greatly reduces the number of mechanicalelements involved.

It is known to use reaction propulsion which utilizes a compressordriven by a turbine. Such devices utilize a portion of the pressurefurnished by the compressor and a portion of the energy produced bycombustion chambers located between the turbine and the compressor, theexhaust gases of the turbine being conducted through the hub of therotor and through a system of pipes through the blades to jets situatedat the extremity of the blades Where the gases are finally expelled andfurnish the reaction which produces the desired rotation of the rotorblades. These known propulsion devices present numerous seriousinconveniences.

The turbine necessitates quite a high temperature in order to operatewell. The obtaining of such a high temperature is difiicult for thefollowing reasons: Because of the high temperature and of the lowpressure, the specific volume of the exhaust gas is so large that theblades of the helicopter need to be much larger than can operate atmaximum aerodynamic efficiency, and particularly if one takes intoconsideration the fact that reaction propulsion necessitates high linearspeeds at the extremity of the blades.

Another diificulty is involved in constructing the rotor hub with itsconduits and its articulated joints conducting the gas in the blades ina manner so that it can function at high temperature. The samedifficulty is present with the blades.

Another trouble is the considerable waste of energy due to the coolingof the gases caused by the large surfaces of the blades.

Certain of these difliculties do not exist where the turbines orcombustion chambers are disposed in the extremities of the blades, butsuch dispositions give rise to serious gyroscopic problems as well asweight problems involving the inertia of the blades.

The principal feature of the present invention consists in utilizing asthe reaction fluid for propulsion compressed air taken between thecompressor and the combustion chambers, the latter serving at the sametime to heat the remainder of the compressed air which drives theturbine, which in turn drives the compressor. Preferably, the airdirected to the reaction jets is first heated in a heat exchangertraversed by the exhaust gas from the turbine and recovering the heatcarried by these gases.

It is a primary object of the invention, accordingly, to provide areaction system as described in the preceding paragraph.

This improvement presents several advantages. From the beginning thethermodynamic cycle is, from the point of view of efficiency, almostindependent of the pressure of the compressor and of the temperature ofthe burners or combustion chambers. The compressor can be used at lowpressure and consequently can be light in weight. The temperature of theturbine can be lower than the temperatures that are usually necessaryresulting in, from the point of view of the resistance of the materialsused, important advantages in safety, advantages which are veryimportant in. aeronautics generally, both in helicopters and in ordinaryaircraft. Because of the fact that the turbine functions at atmosphericpressure, it is easy to cool, for example by means of a special smallcooling fan blowing air from the atmosphere on to the turbine wheel.Cooling can also be carried out by making the turbine blades hollow sothat they suck in air at the center of the turbine rotor and blow it outat their outer ends, operating as a centrifugal ventilation system.

In a helicopter constructed in accordance with the invention, the crosssectional area of the conduits located within the rotor blades for thepurpose of conducting the reaction fluid can be small because of thehigh pressure of the fluid and of its low temperature, even after takinginto account the necessity for reducing to a minimum the losses takingplace through friction. The invention permits the avoiding of theincrease in the cross sectionties caused by unburned products ofcombustion as in systems where the products of combustion are directedthrough the helicopter blades. Also, the temperature of the blades ismoderate.

The free escape of the exhaust gases from the turbine produces a slightthrust, as does the gas being cooled. This thrust can be used forcontrolling the orientation of the helicopter about a vertical axis, asby blowing these gases on the control surfaces or by conducting them toreaction jets directed to port and starboard.

Another object of the invention .is to provide improved stability inhelicopters by utilizing the gyroscopic forces inherent in the highspeed rotation of the turbine and compressor. This obviates the need forspecial heavy gyroscopes which have previously been used for stabilizinghelicopters. In securing the gyroscopic eifect of the.

turbine and compressor, it is advantageous to locate the turbine and thecompressor coaxially with the hub of the helicopter rotor.

The above and other objects of the invention will be apparent from thefollowing specification and the accompanying drawings, in which Fig. 1is a schematic vertical section through the rotor of a helicopter andthrough a turbine and compressor device for directing reaction fluid tothe rotor blades;

Fig. 2 is a vertical sectional view through a helicopter showing amodification of the embodiment shown in Fig. 1, the modification havingthe axis of the turbine positioned vertically. This figure also shows asimple device for orienting the helicopter about its vertical axis;

Fig. 3 is a perspective view of the tail of a helicopter showing anarrangement for directing the exhaust gases Fig.5 is a crosssectional'view taken through aflexible particularly adapted for usewithhelicopter rotor blade the invention;

com-

Fig. 6 is a detailed longitudinal section view taken through a portionof Fig. 8 and somewhat enlarged;

Fig. 7 is a cross sectional view through a rigid type of blade for usewith the invention; and

Fig. 8 shows a form of the novel reaction propulsion system describedherein applicable to use with ordinary aircraft.

In the preferred form of the invention shown in Fig. 1 a compressordischarges compressed air through tubing 21 to a heat exchanger 22 wherethe compressed air passes about the tubes of the heat exchanger and outthrough an outlet 23. The air passing from outlet 23 is divided into twoportions, one portion passing upwardly through tube 24 through the hub25 at the rotor, and outwardly through hollow rotor blades 26, until itis finally discharged through jet nozzles 27 at the ends of the rotorblades.

The other branch 25 of the tubing connected to the outlet 23 contains aburner 26 for fuel supplied through tube 27' for ignition by igniter 28.The products of combustion are directed against the blades of a turbine29 from which the gases pass through the tubing of heat exchanger 22where they heat compressed air being passed into the heat exchangerthrough tube 21.

Both the compressor 20 and the turbine 29 are mounted on a single shaft30, and a small fan 31 may be mounted on a shaft 32 to draw in coolingair through an air intake 33 and direct the air against the turbine 29.After striking the turbine the cooling air passes outside the intake 33which is centrally positioned with respect to and spaced from heatexchanger 22.

A throttle 35 is conveniently positioned in passage 24 so that thepassage may be closed during starting of the device so that all thecompressed air goes to the turbine. Starting may be carried out by anelectric motor (not shown) or even manually through a crank and step upgear.

The system shown in Fig. 1 has numerous advantages over the prior art.The thermodynamic cycle is, as regards efliciency, practicallyindependent from the pressure of the compressor and the temperature ofthe burners. For this reason, low pressure compressors can be used,making the use of light weight parts feasible. The turbine temperaturecan be relatively low with the obvious advantages of such lowtemperatures. The rotor blade cross sectional area can be relativelysmall due to the high pressure of the driving medium and its lowtemperature. The reaction fiuid carried through the hub of the rotor andthe blades is merely heated air so that the difficulties with residuesinherent in the use of exhaust products of combustion for driving rotorblades are obviated. Since the turbine operates under atmosphericpressure, its cooling is a simple matter, for example, the use of smallfan 31 drawing air in through an axial tube in the center of the heatexchanger and expelling along the exterior of the tube after the air hashad cooling contact with the turbine blade. Cooling could also beaccomplished by the use of hollow turbine blades connected to a centralair intake and operating to expel the cooling air centrifugally throughopenings at the outer ends of the blades of the turbine. The relativelylow temperature of the hot air passed through the blades permits theblade temperature to be moderate. Another advantage which will bediscussed in more detail presently is the fact that the exhaust from theturbine can be used to produce thrust for controlling the orientation ofthe helicopter.

In the modification shown in Fig. 1, the axis of the turbine andcompressor is disposed horizontally. This axis can also be positioned ina vertical manner, as for instance in alignment with the axis ofrotation of the rotor blades 26 about hub 25 (Fig. 2). Such a verticaldisposition permits use of the'gyroscopic effect of the turbine andcompressor which are, of course, rotating at high speed, to increase thestability of the helicopter;

thereby doing away with the gyroscopic masses which have been previouslyutilized for this purpose. The weight of the separate gyroscopicstabilizer is thus reduced to the weight of the turbine and compressor.This vertical disposition also permits use of a double brake arrangementfor controlling the orientation of the helicopter about the verticalaxis.

Such an arrangement is shown schematically in Figure 2 in which thefuselage of the helicopter is suspended by a cardan joint 61 at thehollow hub 62 about which turns the rotor 63, and which carries theturbine and compressor unit in such a manner that the shaft 64connecting the compressor 65 and the turbine 66 is coaxial with therotor.

The means for controlling the orientation of the helicopter about thevertical axis includes annular braking surfaces 67 and 63 rotating,respectively, with a rotating part of the rotor hub, and with theturbine, the turbine in this case being constructed to rotate in adirection opposite to the direction of rotation of the rotor. Ifdesired, the annular braking surface 68 may be solidly connected to therotor of the turbine.

Brake shoes 69 and 70 cooperate, respectively, with the annular brakingsurfaces 67 and 68, hydraulic cylinders 71 and 72 being provided forurging the brake shoes against the braking surfaces as desired. The twocylinders 71 and 72 are remotely controlled by control cylinders 73 and74 having internal pistons movable by a hand lever 75 which is pivotedat a point 76 positioned between the two cylinders 73 and 74.

It will be obvious from Figure 2 that when the handle of lever 75 ismoved to the left in Figure 2, the piston of control cylinder 73 will bemoved to the right to cause bydraulic cylinder 71 to press brake shoe 69against braking surface 67.

On the other hand, the reverse movement of lever 75 causes brake shoe 70to be urged against braking surface 68.

With this construction, when brake shoe 70 is applied against brakingsurface 68, the helicopter tends to turn in a direction opposite to thedirection of rotation of the rotor. On the contrary, the pressing ofbrake shoe 69 against braking surface 67 causes the helicopter to turnin the direction of rotation of the rotor.

In the construction shown in Fig. 2, the exhaust from turbine 66 isdirected through a heat exchanger 88 and then outwardly in a downwarddirection through an opening 89 in the bottom of the fuselage of theaircraft, opening 89 being preferably in vertical alignment with thecenter of gravity of the aircraft. This arrangement permits theutilization of the thrust from the exhaust gases to supplement the liftof the rotor. This thrust can be increased in case of emergency byincreasing the output of the compressor, for example by an increase inthe amount of fuel fed to the burner 90.

In Fig. 3 there is shown another means for maneuvering the helicopterabout a vertical axis during stationary flight (hovering), thiscomprising the blowing of the exhaust gases leaving heat exchanger 22 ofFig. 1 through suitable ducts 93 against the rudder 94 of thehelicopter.

These exhaust gases could also be directed to nozzles pointing towardport and starboard and removed from the center of gravity of theaircraft to cause turning of the aircraft about its vertical axis duringhovering. A nozzle directed toward the port side of the aircraft isindicated at 95 in Fig. 3.

Both of the control systems illustrated in Fig. 3 can also be used withthe turbine arrangement shown in Fig. 2 if desired.

111 a helicopter of the type disclosed herein in which the rotor bladesare driven by a passage of heated air through the blades and out of jetnozzles at the end of the blades, it is somewhat desirable to use asmaller number of blades than in the ordinary helicoptersothatthe'bladescan each be constructed with a larger cross-sectional areato'facilitate the passage of hot air through the blades If the number'of blades were to be decreased by reduction to a third of the originalnumber, each blade would then need to be three times as wide, that iswould have to have a chord three times larger, if equal density is to beobtained. The total section is then three or nine times as large as thesection of each individual blade of the rotor having the original largenumber of blades. The total section, therefore, is three times larger.It is thus apparent that the size of the total section increaseslinearly with the decrease in the number of blades at equal density.

The use of rotors having smaller numbers of blades presents vibrationproblems. In the case of helicopters having mechanically driven motorsit is known to fix the rotor hub and the engine all on one integralpart. This part which vibrates during flight will have a neutral pointin which the fuselage is mounted in rubber. The same arrangement can beused with the jet engine described herein, but it would be preferable tofix the jet turbine to the fuselage or rotor hub and use another heavyobject which is located at a sufficient distance from the rotor hub as abalancing weight, for example the landing gear.

Such an arrangement is shown in Fig. 4 in which 100 is the compressorand 101 is the turbine. Radiator 102 is connected to a tube 103 forpassing the heated air through an elastic connection 104 to bearing andsealing means 105, and thence to hollow rotor blades 106 and nozzles107. A hinge 108 connects the fuselage to the neutral point of the rotorand landing gear block for landing gear 109. A fuel tank is indicated at110 while the pilot seat and controls are indicated generally by thenumeral 111.

In the construction of helicopter blades, it is known that the bladescan either be rigid and strong enough to resist the bending stressescaused by aerodynamic forces, or they can be flexible, in which casethey need not resist the bending stresses.

In Figs. and 6 there is shown a new type of flexible blade in whichthere is an outer sheet 120 and an inner steel sheet 121. The innersheet is formed with spaced grooves or corrugations 122 extendingentirely about the circumference of the blade. Corrugations 122 give theinside sheet a high resistance against pressure from the inside and atthe same time permit considerable bending, so that most of the bendingstresses must be carried by the outside sheet 120 which should be of amaterial having a low coeflicient of elasticity, such as plastic oraluminum. The outer sheet 120 lies against the bottoms of thecorrugations 122 and the hollow spaces 123 between the two sheets arefilled with an insulating material. It will be apparent that the hot airpassed through the blade passes through the hollow center 124 of theblade.

In case it is desired to use a rigid blade with the helicopter, adesirable blade of this type is shown in Fig. 7 in which a steel spar orlongeron 130 carries the bending stresses. On the front and rear of thelongeron 130 (leading and trailing edges) there are attached, forexample, by electrical welding, leading and trailing structures 131 and132. Structures 131 and 132 and, if desired, longeron 130, contain aseries of hollow tubes 133 which extend the length of the blade for thepurpose of carrying the hot air to the nozzles at the end of the blades.Tubes 133 are constructed in such a manner that they resist tensionsproduced by internal pressure but do not resist the effects of bendingstresses. For this reason the tubes 133 can be made of very thin andlight weight material. The outer shells of the leading and trailingstructures 131 and 132 are indicated by the numerals 134 and 135.Insulation may be placed in the space between tubes 133 and shells 134and 135.

In Fig. 8 I have shown an axial sectional view of a reaction propulsiondevice of the type disclosed herein as applied to an ordinary aircraft.In this figure, air enters by an intake 145 and is compressed by acompressor 146 and directed through tubing 147 to a heat exchanger 148.The air heated by the heat exchanger is divided into two portions, oneportion passing to a conduit 149 which contains a burner 150. Theproducts of combustion of the burner pass through and drive a turbine151 which in turn drives compressor 146 by means of a shaft 152. Theproducts of combustion pass from tubing 151 through the tubing of heatexchanger 148 and then out through a nozzle 153 directed rearwardly withrespect to the aircraft. The other portion of the air passed through theheat exchanger 148 is directed rearwardly through another nozzle 154also directed rearwardly. Turbine 151 is cooled by air taken in throughan inlet 155 and blown against the turbine by a fan 156 driven by theturbine. Air from inlet 155 passes through an axially positioned tube inwhich fan 156 is positioned, and after operating upon turbine 156, thecooling air passes rearwardly outside the inlet tube and is intermingledwith the products of combustion passing out of nozzle 153 in such amanner that a suction is produced in exit tubing 157 which assists inthe flow of cooling air. If desired, auxiliary burners or other heatingmeans could be located in nozzle 154.

The auxiliary burners or other types of heating means just referred toand also mentioned previously herein are particularly useful when anemergency surge of power is needed. In the case of helicopters, it isalso feasible to locate combustion chambers or other heaters near theblade tips for heating the air being passed to the blade nozzles.

I wish it to be understood that the construction I have described hereinis shown only in an exemplary sense and is not to be construed as theonly manner of carrying out my invention. It is my intention to coverall modifications falling within the inventive concept as defined by theappended claims.

I claim:

1. A reaction propulsion device for a vehicle, comprising a compressor,a heat exchanger having an inlet connected to receive the output of saidcompressor and an outlet for the fluid entering at said inlet, a'conduitreceiving fluid from said outlet, said conduit being divided into twobranches, combustion means in a first branch of said conduit, a turbinedrivably connected to said compressor, means for directing thecompressed fluid and exhaust gases from said combustion means againstsaid turbine to drive the turbine, means for passing said exhaust gasesand compressed fluid from said turbine to said heat exchanger to heatthe fluid entering said inlet, helicopter blades mounted on a vehicle,at least one of said blades having an internal passage in communicationwith said second conduit branch to receive heated propulsion fluidtherefrom, and a propulsion nozzle in said blade in communication withsaid internal passage, said heated fluid being expelled through saidnozzle to cause rotation of said blades, said compressor and turbinebeing rotary and arranged coaxially with the axis of rotation of saidhelicopter blades, whereby the rotation of said compressor and turbineexerts a gyroscopic effect having a stabilizing effect on thehelicopter.

2. A reaction propulsion device for a vehicle, comprising a compressor,a heat exchanger having an inlet connected to receive the output of saidcompressor and an outlet for the fluid entering at said inlet, a conduitreceiving fluid from said outlet, said conduit being divided into twobranches, combustion means in a first branch of said conduit, a turbinedrivably connected to said compressor, means for directing thecompressed fluid and exhaust gases from said combustion means againstsaid turbine to drive the turbine, means for passing said exhaust gasesand compressed fluid from said turbine to said heat exchanger to heatthe fluid entering said inlet, helicopter blades mounted on a vehicle,at least one of said blades having an internal passage in communicationwith said second conduit branch to receive heated propulsion fluidtherefrom, and a propulsion nozzle in said blade in communication withsaid internal passage, said heated fluid being expelled through saidnozzle to cause rotation of said blades, said compressor and turbinebeing rotary and arranged coaxially with the axis of rotation of saidhelicopter blades and arranged to expel the exhaust gases from saidturbine in said axial direction downwardly, whereby the'rotation of saidcompressor and turbine exerts a'gyros'copic' effect having astabilizing'effect on the helicopter andthe'downward expulsion ofexhaust gases exerts an'upward thrust on the helicopter.

3. A reaction propulsion-device for 'a"vehic1e,c'0mp'rising acompressr,'a'heat exchanger having an inlet connected to"re'c'eive theoutput 'of said compressor and an outlet for th'e'fiuid entering at saidinlet, a conduit receiving fluid from said outlet, said conduit beingdivided into two branches, combustion means in a first branch of saidconduit, a turbinedrivably'connected 'to" said compressor, means fordirecting'the'comp'rcssed fluid and exhaust gases from saidcombustionmeansagainst said turbine to drive tion with said internalpassage, said heated fluid being expelled through said nozzle to causerotation "of said blades, a rudder on said helicopter, and means fordirecting the 8 exhaust gases from said turbine against said rudder,whereby orientation of the helicopter about a vertical axis is achievedduring hovering.

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